This invention relates to a combined radial-axial slide bearing.
A possible form of a liquid-lubricated axial slide bearing is a hydrostatic bearing whereby use is made of an external power source supplying the liquid under pressure to the slide bearing.
This liquid is brought into the bearing by means of a flow restrictor or restrictor, such as a capillary or a small opening.
The principle of such hydrostatic bearing is based on the fact that, when the gap of the bearing becomes smaller, the flow diminishes and the pressure drop over the restrictor is reduced. The pressure in the gap increases, and the force which caused the gap to narrow is compensated.
These hydrostatic bearings have a high loading capacity depending on the feeding pressure of the liquid, a high stiffness and a carrying capacity which is little dependent on the number of revolutions.
Especially if the lubricating liquid has a low viscosity, such as water, this restrictor, however, has to be very small, as a result of which this latter becomes very sensitive to obstructions.
In such bearing, the tolerances are very narrow, especially with water, in consideration of the fact that, in order to limit the flow rate, the gap of the bearing has to be as small as possible.
Moreover, due to this restrictor, the construction of the axial bearing is rather complex and this bearing is expensive, whereas in most cases a pump has to be applied in order to obtain sufficient pressure.
One of the forms of a radial slide bearing lubricated with a liquid is the hydrodynamic bearing, whereby the movement of the axle itself provides for the necessary pressure of the lubricating liquid.
The bearing surrounds the axle with a little play in between. When a radial force effects on the axle, the axle will situate itself excentrical, as a result of which a wedge is formed. Under the influence of the revolving movement of the axle, the liquid is pressed into this natural narrowing, as a consequence of which a pressure build-up is resulting. This pressure build-up will lift the axle and provide for that the force which displaced the axle is counteracted. Thus, it is so that in balance, the axle will not be centered, as otherwise no pressure could be build up. Ideally, the excentricity is between 60% and 90%.
Such hydrodynamic bearings are rather simple and inexpensive, although they require narrow manufacturing tolerances. They are operationally reliable, however, they have no high loading capacity and rigidity. It is, however, disadvantageous that their loading power depends on the number of revolutions and that, during starting, there is a contact between the axle and the bearing and therefore wear and tear does occur.
It is, however, also known to combine a hydrostatic axial and a hydrostatic radial bearing to a single slide bearing.
Such combined radial-axial slide bearing is described, amongst others, in the British patent No. 639.293.
An axle which is provided with two collars in between which a stationary ring with a small play is provided and which is provided with a number of recesses in its internal circumference, at which, by means of a restricting mouthpiece, a restrictor is formed and to which a fluid, such as air or steam, is supplied.
This fluid flows through the recesses up to the collar and thus forms a fluid layer around the axle, such that this latter is radially borne. This fluid flows radially outward through the gap formed by the play between the extremities of the ring and the collar and prevents the contact between the ring and the collar or, in other words, provides for the axial bearing.
In fact, the aforementioned British patent describes a hydrostatic radial bearing which is fed by means of several narrowings feeding to different chambers around the bearing. Instead of feeding the hydrostatic axial bearing by means of a separate narrowing, use is made of the narrowing which is formed by providing the narrowing of the radial bearing in series with the radial bearing itself.
Due to the presence of the mouthpieces forming a narrowing or restrictor, this known combined bearing, however, possesses the same disadvantages as the aforementioned axial bearings, with thus, amongst others, the danger of obstruction of these narrowings.
The invention aims at a combined radial-axial slide bearing which does not show these disadvantages and therefore causes no danger of obstruction of a capillary or mouthpiece and which is relatively inexpensive and compact.
According to the invention, this aim is achieved in that the combined bearing is composed of, on one hand, a hydrodynamic radial slide bearing which surrounds an axle to be beared with a play, such that between the axle and the radial slide bearing, a first gap is formed, which first gap is in connection with a source of liquid under pressure and, on the other hand, at least one hydrostatic axial slide bearing which, with a play, is situated opposite to a radially extending surface portion of the axle, such that also between this last-mentioned surface portion of the axle and a radially-directed portion of the axial slide bearing, a second gap is formed, whereby this second gap is in connection with the first gap, such that this axial slide bearing is fed by means of the first gap and this first gap fulfils the function of restrictor for the axial slide bearing.
In that the first gap takes the function of restrictor for the axial slide bearing, no external restrictor is required, such that all above-mentioned disadvantages, which are a consequence of such external resistor, are eliminated.
The first gap and the second gap do not necessarily have to be in direct connection with each other. They can do so by means of a chamber between the axle and a bearing housing.
A portion of this housing can border the gaps directly. The housing can be provided also at the inside with one or more bearing cushions or such, which border a gap.
The combined bearing can be singular and comprise a single axial slide bearing at an extremity of the radial bearing, whereby, thus, the second gap is in connection with one extremity of the first gap, however, in a variant this combined bearing is double-sided and comprises two axial slide bearings, one at each extremity of the radial slide bearing, whereby the second gaps of the two axial slide bearings are in connection with respectively the two extremities of the first gap.
In this latter case, the connection of the first gap to the source of liquid under pressure preferably gives out in the center of the first gap on two locations which are situated symmetrical in respect to the middle of the first gap.
In the other case with one axial bearing, the aforementioned connection can give out at any location in the first gap, whereby the pressure drop in this gap for one and the same flow rate of liquid depends on the position of this location.